1. Field of the Invention
This invention relates to the field of epoxy traffic marking compositions and more particularly to a composition and method for improving the cure time of such traffic markings.
2. Description of the Related Art
Epoxy binders currently used in traffic markings consist of two parts. One part (often called resin part or part A) is a formulation containing epoxy monomers or oligomers along with white or yellow pigments. The second part (called part B or hardener) is a formulation of one or more chemicals such as amines, phenols, alcohols or their derivatives. When two parts of resin (part A) and one part of hardener (part B) are mixed, a reaction takes place between the epoxy resin and the hardening agent resulting in a polymerization of epoxy. Once the polymerization completes or nearly completes, the whole mixture become very hard (cured epoxy resin). The mixing ratio of the two parts can vary depending on the formulation.
These epoxy binders are used in many types of coatings on substrates like floor, concrete, metal, plastic and other surfaces. They are also used as highway traffic markings. Some examples of commercial epoxy binders in traffic markings are LS-50, LS-60, and LS-65 from Epoplex company; Poly-Carb Mark 55, Poly-Carb 55.2, Poly-Carb 55.3, Poly-Carb Mark 55.4, Poly-Carb Mark 55.6 from Dow Chemicals; Ennis HPS-2, Ennis HPS-3, and Ennis HPS-4 from Flint-Ennis; and the corresponding hardeners are sold under the same name. Epoxy traffic markings offer good durability and excellent protection from ultraviolet ray degradation. Epoxy binders, especially slow set epoxy binders, flow well on asphalt and concrete surfaces, fill all gaps in asphalt and concrete surfaces and give a good surface over which retroreflective glass beads can be applied.
In some applications, it is desirable to speed up the hardening of the epoxy composition through the use of curing agents. In general, many classes of chemicals have been used as curing agents for epoxy during the past 50 years. Some examples of classes of chemicals are amines, alcohols, phenols, acids, metal salts, and a combination of one or more of these classes.
U.S. Pat. No. 3,642,649 describes the use of salts prepared from tertiary amine and acids like hydrobromic acid or toluene sulfonic acid as curing agents. These amine salts cure epoxy resin at low temperatures (40 to 70° F.) which takes several hours to cure.
U.S. Pat. No. 4,162,358 describes the use of aromatic amines as curing agents for epoxy at 80° C. and above.
U.S. Pat. No. 4,273,914 describes the use of carboxylic acid anhydride and Lewis acid complex as a fast curing agent for epoxy compositions. These are mainly for electrical applications where the Lewis acid catalysts are from SbCl5, BF3, TiCl4, SnCl4, and their mixtures. The cure time at room temperature is more than 36 hours.
U.S. Pat. No. 4,629,742 describes the use of mannich bases (beta-amino-ketones) as curing agents,
U.S. Pat. No. 4,668,736 describes the use of metal salts as curing agents, particularly nitrates and perchlorates. Calcium nitrate is studied in detail.
U.S. Pat. No. 5,508,373 describes the use of various aliphatic and cycloaliphatic amines as curing agents (hardeners) for epoxy.
U.S. Pat. No. 5,746,935 describes the use of various alcohols and their derivatives as curing agents for epoxy.
U.S. Pat. No. 5,958,593 describes the use of a mixture of aliphatic amine and metal salt, like calcium nitrate, as a curing agent.
U.S. Pat. No. 6,987,161 describes various mixtures of chemicals as curing agents for epoxy. The mixtures of chemicals are from classes of amines, hetero aromatic amines, diamides, primary amines, tertiary amines, acids, phenols, and alcohols. This patent also teaches how the mixture can change the curing temperature and rates,
U.S. Pat. No. 6,911,109 describes how a polymer of acrylic monomer when mixed with epoxy improves the properties of the final composite. The curing agents (hardeners) disclosed are similar to those discussed herein.
U.S. Pat. No. 7,358,312 describes the use of heterocyclic-based amines and their mixtures with other amines.